Carrier-transmission system



L. E$PEN$CHED CARRIER TRANSMISSIO?! SYSTEM Filed Juna 13, 1919 INVEN TOR. A L Eemefiz'e BY I k ATTORNEY W .c. .1 Presenters Application files June 13,

To all whom it may concern:

Be it known thstl LLOYD Esrnnsornnn residing; at l-lollis, Long lsland, in the county of Queens and State of New York, have invented certain improvements in Currier- 'l'runsinission ysteuis of which the following' is a specification.

This invention relates to transmission systems in which carrier currents are employed for the transmission of low frequency sis,- nals such as telegraph or telephone signals.

This invention provides -i cans whereby a plurality of low frequency circuits may he interconnected for the transmission of carrier frequencies from one to the other while maintaining the two systems electrically distinct with regard to low frequencies.

It further comprises means whereby the carrier currents of one or more carrier chemo nels may he superposed on a low frequency circuit. and after being transmitted over s desired section of the circuit may be transferred to another low frequeinty circuit for transmission over the letter, without necessir toting any. reorganization of the low frequency circuits involved.

lit also comprises an arrangement whereby a plurality of transmission circuits adapted for the transmission of a "plurality of frequencies (among which only be included carrier frequencies for a plurality of cornmnnicution channels) may interconnected the transmission of certain frequencies in'tundein over the circuits, at the same time maintaining the circuits:electrically \distinct with reference to other frequencies,

.so that such other frequencies are not tronsinittcd from one circuit to the other. v

These aims. well as other objects more fully hereinafter appearing are secured in accordance with the present invention by providing a system oi filters so arranged thngt two transmission circuits interconnectcd'through u filter adapted to transmit the frequencies which it is desired to trans fer from one circuit to the other while era eluding other frequencies. rlsA i'i'urther retinemcnt. filters may elso he n l-ranged in those portions of the circuits 'over which it is desired that the transi erre'd frequencies shall not he trnnsniitted, said filters being so designed as to exclude the frequencies whici are to he trens ferred ironi cir cuit to the other while transm tting frequencies which are not to he so trsnsrerred.

points which are loaded for low frequency transmission, or which may be constructed of cable, in either of which cases the circuits considered in their entirety would not he adopted for transmission of carrier fre quencies, although portions of the circuits would be available for this-purpose. If then there should he another circuit or a section of another circuit adapted for the trsnsniission carrier frequencies extending from the distant point to an intermediate point which is connected to the first point by sections of the through circuits which are adapted for carrier transmission, a through carrier circuit may be provided by establishing a carrier connection between the available section of the-line terminating et the distant station and an available-section or some one of the lines extending from the. station. i

In other instances it may he desired to provide carrier transmission between two points which are not interconnected by through circuits from one point to the other. in such :1 case, advantage may be taken of the fact that connections extend from the first point through an intermediate point to sonic third point while otherchnnections extend from the second point through the intermediate point to a fourth point. By providing a carrier transmission connection between sections of the circuit extending from the first second points through the intermediate point to other mints, a carrier transmission circuit may e established between the first and second *points.

The invention may now he iniorefully understood by reference to the following (lescrigtion when rend in connection with the accompanying drawing. l igure 1 of which is s schematic diagram showing one situation to which the principles of the invention he applied, Fig. lot which is a, circuit 30 case in which the line circuits adapted for carrier transmission are available. A transmission line Mir- L1 is illustrated as extending from station A through an intermediate station E to a third point D, the section ML of this line being of such character that the carrier frequencies may be transmitted thereover. Another line MLT,L is also shown as extending from station (J through intermediate station B to another point of this line, being also adapted $0 for the transmission of carrier frequencies.

By interconnectingthe .two sections ML and ML by a'carr er transmission path as indicated in dotted lines at B, a through carrier transmission circuit between stations A.

and (J may be provided.

The above situation is typical of the general condition which it is proposed to meet by means of the presenlt invention. The un-, (erl ing it ea'is e ual a licable to the y q M 'l ll, for instance, extends through from station A to C, but the section T L, by reason of being loaded for low frequency transmission, or by reason of the fact that it is constructed of 3-3 cable, is unavailable for through carrier transmission. In such case the section ML may be extended over a carrier connection at the intermediate station Etc 3. section such as ML of a line extending from station C to 40 intcrmediate'station B, or through said station to any other oint, assuming, of course, that the section is adapted for the transmission of carrier currents.

Turning now to the circuit organization which is shown in more detail in ig. 2, ML

represents a section of an ordinary low frequency transmission line which is adapted for the transmission of carrier currents, said section extending between stations A and B.

to At station B the line which includes the section ML is extended over another section T,L to some distant point which is not involved in the carrier transmission path which it is desired to establish. At station A the-line which includes the section ML may be extended over a terminal section LT. In a similar manner ML designates a section of low frequency transmission line which section extends between. stations B Q and '1) and is also adapted to transmit carrier frequencies. The line including; the section ML is extended at station B over a section 'l,L and at station C over terminal seetion LT. In order to establish a through csrrier connection between stations A and C,

sesame the section ML and ML may be interconnected intermediate station B through a high frequency filtering arrangement H F which is so arranged as to transmit the desired carrier frequencies while substantially suppressing other frequencies. In orderto prevent the transmission of carrier frequencies over the line sections T,L and T L, low frequency filters l l l and L l may be included in these sections, said filters being so designed as to substantially suppress carrier frequencies which it is desired totransfer from the section ML to the section ML, while freely transmitting such frequencies as it is desired to transmit from the section ML to the section T 11 or from the section ML to the section T L.

The filters which are used in the combination just described may be of any desired character, the only requirement being that they shall transmit the desired ranges of fre quencies to the substantial exclusion of other frequencies. Preferably these filters should be of the general type disclosed in United States Patents granted to George A. Campbell, Nos. 1,227,113 and 1,227,114 dated Way 22. 1917.

The arrangement of filters is shown in more detail in Fig. 3 in which the filter il F interconnectingthc line sections ML and ML is illustrated as consisting of a plurality of sections having series capacity and shunt inductance so provided in accordance with theprinciplcs set forth in Campbell patents above referred to as to transmit a band of frequencies between whose limits are included the. frequencies which it is desired to transfer from the section lv'lL to the section ML. if, for instance. the line including the sections ML and T,L and the line including the sections ML and T,L are ordinary transmission lines, the filter H,F

would be so designed that its lower cut-offfrequency would be at 'some point above the upper limit of the frequencies used in ordinary telephonic transmission. so that carrier frequencies above this limit would be freely transmitted. while frequencies below the upper limit of telephonic transmission would be suppressed.

The filters L} and LF are each illustrated as comprising a plurality of sections. each including series inductance and shunt capacity so proportioned as set forth in the Campbell patents above referred to as to freely transmit a band of frequencies below v an upper limiting frequency and substantially suppress frequencies lying aboye said limit. In the case already referred to, in which the lines are ordinary transmission lines, the filters L1 and LE would be arranged with a cut-off frequency at or above the highest frequency used in ordinary telephonic transmission.

It will be clear, therefore, that with the I accents arrangement so fardescrihed, frequencies lying within the limits oi ordinary telephonic transmission may be transmitted from section ML over section "LL without any substantial transmission loss due to the connection between sections ML and .ll llL through the filter Fl F. So also frequencies Within these limitsniuy be transmitted from section ML over section T 1). Carrier frequencies or other frcquencies ahove the linitelephonic transmission may be transmitted from section ML to section ML or vice versa through the filter E l Without involving any substantial transmis sion loss due to leakage through the filter L l? or L,F'.

The low frequency transmission lines may he of any character so far as their utility is concerned, that is, they may he either telephone finest-telegraph lines or any other form of signal transmission circuit. carrier system superposed upon these lines may also be adapted for the transmission of any desired kind of signals, and, so far as principle of operation is concerned, may he its of ordinary of any type known in the art. For pur poses of illustration, however, terminal carrier apparatus of the general type shown and described in thellnited States patent applications of B. W. Kendall, Serial No. 130 50, tiled November 9, i918 and 131592 filed December 18, will, which has become Patent No. 1,445,141, dated Feb. 13, 1923-, is schematically illustrated and will. now he described.

The terminal carrier current apparatus comprises a carrier hranch CB which is associated with the main line, section hill through a high frequency filter similar in character to the filter Pi l already de scribed, the function of this filter being to suppress low frequency currents from the carrier apparatus. in order to prevent the transmission of carrier frequencies to the terminal portion of the line Lil, a low rrequency filter LP, similar to the filters ill- F and L,F"already described. may he providcd. The carrier branch GB is associated With a common carrier transmitting circuit TL and the common carrier receiving circuit Rll'throfig'h a transformer 10. The circuits TL-and' Eli are so arranged as to he conjugate with respect to each other or, in other ords so that electrical operations in the one circuit will be without effect upon the other. This result is secured by providing a circuit including a network FN for balancing the filter HF and another network N for balancing the main line and other apparatus connectedto terminals of the carrier branch CB.

A plurality of carrier transmitting channels TL TL TL, and "EL, may he associated with the common carrier transmitting circuit TL, and similarly carrier The ceiving channels RL EL EL, and BL, are associated with common carrier receiving circuit llli. Each corresponding transniitting and receiving channel is associated with a low frequency transmission line such as i L etc. through transformers ll, l2, l3 and ll and corresponding transmitting and receiving channels are rendered conju gate with respect to each other by providing lmlaucinn networks such as N N N, and N, for the correspondiiug' low frequency lines.

Each transmitting channel such as TL, is provided with translating apparatus for supplying the several carrier frequencies, modulating these frequencies in accordance with the low frequency signaling currents from the low frequency lines L L etc. and for impressing the modulated cies upon the common transmitting circuit TEL These arrangements may he o'li'any desired character, such as, for instance, those shown in the applications of B. W. Kendall above referred to, and are schematically illustrated at Tin. Th TA, and TA In a similar manner the several receiving channels such as EL R1 etc. are provided with means for selectively separating the received modulated carrier frequencies, for demodulating or Cletec g the received oscillations, and for impressing the resultant low frequency signaling currents upon the low frequency lines L L These arrangenients may also he of any Well knowncharacter but are preferably of general type illustrated and describe-cl in said applications of B. W. Kendall.

The carrier apparatus at the station E maybe similar in character to that alreaclv described in connection with station A and need not he further discussed. it heing suiii cient to lrnow that the various elements at station are designated by the same reference character as those at station A, with the exception that the reference characters apnli-ed to the apfaratus at station C are frequencurrents of the several :trequenciesimpressed upon the common transmittingcircuit TL. From these circuits several modulated ire-- quencies are transmitted over the transformer 10 to the carrier branch GB without producing any, substantial reaction upon the receiving ircuit ill). The filter HF freely transmits the several modulated carrier trequencies which are then transmitted over the line section through the filter-H 3 to the line section MU. the filters L 1 and L F functioning to prevent the modulated carrier frequencies from entering the line sect-ions TL and T ll. At the station C the filter Ll prevents the modulated carrier frequencies transmitted over the line section ML from entering the terminal line TL While the high frequency filter Hl/ permits the free passage of the modulated carrier currents to the carrier branch CB. From this circuit the several frequencies are transmitted to the common receiving circuit RL' without producing any suhstantial reaction upon the common transmitting circuit TL. By means of receivingtranslating apparatus HA RA etc, the several modulated carrier frequencies are filtered into their respective channels. are modulated or detected and purified, the resultant low frequency signaling currents heing impressed through the transformer arrangements 11'. l2, l3 and 14 upon the outgoing low frequency lines L L L and 3.. i The operations incident to transmission in the opposite direction will he in all respects similar to those already described and need not be further'discussed.

The several transmitting channels referred to in the preceding descri 'ition Whether low frequency channels or high frequency carrier channels may be employed for the transmission of telegraphic. telephonic or any other form of signals. the essential feature of the invention being the provision of arrangements whereby certain frequencies may be transferred from one transmission circuit to the other. While the transmission circuits are maintained electrically distinct with regard to other frequencies. Furthermore the filtering means employed for maintaining this relation between the circuits may he of other types than the broad band filters ahove described.

The arrangement above described is capahle of a number of applications other than those above discussed. Thus, for instance by means of this invention a carrier circuit may he extended over a number of successive telephone circuits of shorter lengths. It is also possihlc to extend the carrier circuit over a point of disruption. in the ordinary. telephone circuit such as is occasioned hy the insertion of a telephone repeater in the circuit. the carrier frequencies hcing filtered out and transmitted through a side hranch around the repeater. ln general, junctions hetu'ccn lines or line sections for transmitting carrier frequencies may he made at any points where the lines neighbor cach other whether at the ends of the lines or at intcrnlcdliite points.

'hilc it has seemed desirable for the purpose of clearer ululerstanding. to illustrate the invention as embodied in c rtain specific forms, it will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following: claims.

TV hat is claimed is:

1. in a signaling system. a plurality of transmission lines adapted to transmit voice frequency signaling currents. each lransmission line comprising a plurality of sections at least one of which is adapted to transmit high frequency currents of the order used for carrier transmission. and means to interconnect said lines for the transmission of carrier frequencies from a high frequency section of one line to a high frequency sec.- tion of another line while maintaining the other sections or" the lines electrically sepa rate with regard to thc transmission Oil voice frequency signaling currents. said means in cluding an apparatus adapted to substan tially suppress voice frequency signaling currents.

2. In a signaling system, a plurality of. transmission lines adapted to transmit voice frequency signaling currents. each transmission line comprising a plurality of sections at least one of which is adapted to transmitv high frequency currents of the order used for carrier transmission, and means to inter connect said lines for the transmission of carrier frequencies from a high frequency section of one line to a high frequency section of another line While maintaining the other sections of the lines electrically sepa rate With regard to the transmission of voice frequency signaling currents. said means ineluding an apparatus adapted to substantially suppress voice frerniency signaling currents while freely transmitting frequencies shove the upper limit of frequencies used in the transmission of low frequency signaling currents.

3. In a signaling system, a plurality of transmission lines adapted to transmit voice frequency signaling currents. eat h transmis sion line comprising aplurality of sections at least one of which is adapted to transmithigh frequency currents of the order used for carrier transmission. and means to interconnect said lincs-for the transmission of carrier frequencies from a high frequency section of one line to a. high frequency scction of another line While n'ia-intaining' the other sections of the lines electrically separate with regard to the transmission of voice frequency signaling currents, said means including an apparatus adapted to substantially suppress voice frequency signaling currents While freely transmitting a band of frequencies above the upper limit of frequencies used in the t'ansmission of low frequency signaling currents and in.- cluding frequencies used for carrier transmission",

in a signaling systeime "plurality of transmission lines adapted to transmit voice frequency signaling currents, each transmission line comprising a plurality of sections atleast one oi' Which-is adapted to transmit high "frequency currents of the order used for carrier transmission, and means to interc'onnect said lines" for the transmission of carrier frequencies from high frequency section crone line to ahig'h ."trequchcy section of another line While maintaining the other sections of the lines electrically separate with regard to the transmission of voice frequency signaling currents, said means including a broad band filter adapted to sub stantiallysuppress voice frequency signaling currents While freely transmitting frequencies above the upper limit of frequencies used in the transmission of low frequency signaling currents.

5. in a signaling system, a plurali"y of transmission lines adapted to transmit voice frequency signaling currents, each transmission line comprising a plurality of sections at least one of which is adapted to transmit high frequency currents of the order used for, carrier transmission, and means to interconnect said lines for the transmission of carrier "frequencies from a high frequency section of one line to a high frequency section of another line While maintaining the other sections of the lines electrically separate with regard to the transm'ssion of voice frequency signaling currents, said means including a broad band filter adapted to substantially suppress voice "frequency signaling currents While freely transmitting a hand of frequencies above the upper limit of frequencies used in the transmission of low frequency signaling currents and ingluding frequencies used tor carrier transmisslon.

6. in a signaling system, a plurality of transmission lines adapted to transmit voice frequency signaling currents, each transmission line con'i'prising a plurality of sections at lcast one of which is adapted to transmit high frequency \currcnts of the order used for carrier transmission. and means to interconnect said lines for the transmission of carrier frequencies from a high frequency section of'one lineto a high frequency section of another line While maintaining the other sections o'f the lines electrically sepa/ rate with regard to the transmission of voice. frequency signaling currents, and means in sections adjacent to the interconnected sectionstorsulistantially suppressing the trans mission over said adjacent sections of trequencics shove the upper limit oi frequencies used in the transmission of low frequency signaling currents.

7. ln a signaling system, a plurality of transmission lines adapted to transmit voice frequency signaling currents each transmission line compris ig a plurality of sections at least one of which is adapted to transmit high frequency currents of the order used for carrier transmission, and means to interconnect said lines for the transmissionot carrier frequencies iron: a lli ll ili'cqucncy section of one line to a high frequency sec" tion of another line while maintaining the other sections of the lines electrically separate 'ith regard to the transmission of voice vfrequency signaling currents, said means including an apparatus adapted to substantially sugprcss voice frequency signaling currents While freely transmitting frequencies above the upper limit oi frequencies used in the transmission of low frequency ignaling currents, and means in sections adjacent to theinterconnected sections for substantially suppressing the transmission over said adjacent sections of frequencies above the upper limit of frequencies used in the transmission of low frequency signaling currents While freely transmitting frequencies below said limit.

8; in signaling system, a plurality of transmission lines adapted to transmit voice frequency signaling cin'rents, each transmission line comprising a plurality of sections at least one o l which is adapted to transmit high frequency currents of the order used for carrier transmission, and means to interconnect said lines for the transmission of 'arricr frequencies from a high frequency section of one line to a high frequency section of another line While maintaining the other sections of the lines electrically separate with regard to the transmission of voice frequency signaling currents, and means in sections adjacent to the interconnected scc' tions for sunstantially Sfll'iPliSSlllQ; the transmission over said adjacent sections of frequencies above the upper limit ot frequencies used in the transmission oi. low frequency signaling currents, While freely transmitting a band of "frequencies below said limit.

'9. in a signaling system, a plurality 0'? transmission lines adapted to transmit voice frequency signaling currents, each transmission line com rising a plurality of sections at least one. of which is adapted to transmit high irequency currents of the order used /for carrier transmission, and means to interconnect said lines for the transmission of carrier frequencies from a. high "frequency section-of one line to a. high frequency section (it another line While maintaii'iing the other sections the lines electrically separate with. regard to the transmission of voice i rcquency signaling currents, said means including a'hroad hand liltcr adapted to sulistai'it rihy suppress voice -trequcncy na ling currents ivhiic freely transmitting frequencies shove the upper limit of qu cnc'es used in the transmission of low sion line comprising a plurality of sections at least one of which is adapted to transmit high frequency currents of the order used for carrier transmission, and means to interconnect said lines for the transmission of carrier frequencies from a high frequency section of one line to a high frequency section of another line While maintaining the other sections of the lines electrically separate with regard to the transmission of voice frequency signaling currents, said means including a broad band filter adapted to substantially suppress frequencies below the upper limit of frequencies used in ordinary telephonic transmission while freely trans mitting a band of frequencies above said limit, p 11. In a signaling system, a plurality of transmission lines adapted to transmit voice frequency signaling currents, each transmission line comprising a plurality of sections at least one of which is adapted to transmit high frequency currents of the order used for carrier transmission, and means to interconnect said lines for the transmission. of carrier frequencies from a high frequency section of one line, to a high frequency section of another line while maintaining the other sections of the lines electrically separate with regard to the transmission of voice frequency signaling currents, said means including a broad band filter adapted to substantially suppress frequencies below the upper limit of frequencies used in ordinary telephonic transmission while freely transmitting a band of frequencies above said limit, and means in sections adjacent to the interconnected sections comprising broad band filters adapted to substantially suppress frequencies above the upper limit of telephonic transmission while freely transmitting a band of frequencies below said limit.

12. In a signaling system a plurality of lines adapted to transmit voice frequency signaling currents, means to superpose on said lines a plurality of high frequency carrier channels, means for interconnecting the lines so that high frequency currents will be transmitted from one line to vthe other while the lines are maintained electrically sepa rate with regard .to voice frequency currents, said last mentioned means including a connection between said lines, and means in said ea ers connection adapted to substantially suppress voice frequency signaling currents.

13. In a signaling system a plurality of lines adapted to transmit voice frequency 7 rents, said last-mentioned means including a connection between said lines, and means in said connection adapted to substantially suppress voice frequency signaling currents while freely transmitting frequencies above the upper limit of frequencies used in the transmission of low frequency signaling currents.-

14. In a signaling system a plurality of lines adapted to transmit voice frequency signaling currents, means to superpose on said lines a plurality of high frequency car-. rier channels,-means for interconnecting the lines so that high frequency currents will be transmitted from one line to the other While the lines are maintained electrically separate with regard to voice frequency'current/s, said last mentioned means including a connection between said lines, and means in saidconnection including a broad band filter adapted to substantially suppress voice frequency signaling currents while freely transmitting frequencies above the upper limit of frequencies used in the transmission of low frequency signaling currents.

15. In a signaling system a plurality of lines adapted to transmit voice frequency signaling currents, means to superpose on said lines a plurality .of high frequency carrier channels, means for interconnecting the lines so that high frequency currents will be transmitted from one line to the other while the lines arernaintained electrically separate with regard to voice frequency currents, said last mentioned means including a connection nection including a broad band filter adapted to substantially suppress vdice frequency signaling currents while freely transmitting a band of frequencies above the upper limit of frequencies used in the transmission of .between said lines, and means in said -con-- low frequency signaling currents and inmission.

16. In a signaling-system, a plurality of lines each adapted to transmit ,a plurality eluding frequencies used for carrier transof frequencies, means to interconnect said lines for the transmission ofa definite range of frequencies from one to the other while maintaining them electrically separate with regard to other frequencies, said means comprising a conductive connection between the lines, and a broad band filter in said conned. tron adapted to transmit with uniform negligihle'attenuation a ban-cl oi? :i'recuencies iii from one line to another while suostantis. suppressing other frequencies,

17. in a signalling system a plu'rulity of lines each adapted to transmit plurality of frequencies, means to interco nect seiil lines for the transmission of cos n of said frequencies from one to the other While inaintaining thein clectricaiiy senarate with garcl to the other frequencies, saicl means comprising a conductive connection between the lines, and means in said connection adapted. to transmit certain free;'acncies with uniform negligible attenuation While suicstantially suppressing other frequencies.

In a signaling system a plurality of transmission lines adapted to transmit voice frequency signaling currents each transmission line comprising plurality of sections at least one of which is to transmit high frequency currents of the order used for transmissio and another section of which incapalole of eiiectively transmitting frequencies suhstan tially higher then voice frequencies, and means to interconnect saici lines at stations intermediate the terminal stations thereof for the transmission carrier frequencies from high frequency section of one line to a high frequency section of another line while maintaining the other sections of the lines electrically separate with regard to the transmission of ing currents, Sfiifil incuns including an an paratus adapt-oil to substantially suppress voice frequency signaling currents 19. In signaling sysien plurality of transmission lines to transmit voice frequency signaling currents each transmission line comprising s plurality of tions at least one of much is aclaptecl order used tor carrier ransniissioh and another section of which is incapable of etfectively transmitting itrequencies SUbSc'AH- tially higher than voice frequencies and means to interconnect said lines st stations intermediate the terminal stations thereof for the transmission of carrier frequencies from a high frequency section of one line to a liig h frequency section of another iinc While maintaining the other sections of the lines electrically separate with regard to the )ice frequency transmit high frequency cuircnts of the mission of voice feequency signaling currents, saicl means including a broad banl filter adaptccl to substantially suppress voice frequency signaling currents while freely, transmitting frequencies above the upper limit of frequencies used in the transmission of voice frequency signaling currents.

21in s signaling system, plurality of transmission. lines adapted to transmit voice frequency si isling currents, each trans mission line comprising plurslity of sections at east one of: which is adapted to in transmit high frequency currents of the order used for carrier transmission and another section of which is incapable of ei'lectiveiy transmitting; frequencies substantially higher than voice frequencies, ancl means to interconnect ssid lines at stations inter mediatethe terminal stations thereof for c transmission of carrier frequencies from high frequency section of one line to a high frequency section oi. another line While maintaining the other sections of the-lines electrically separate with regard to the transmission of voice frequcncy'signaling currents, and means in sections adjacent to the intercoi'inectecl sections for suhsta-ntially the traiss iiission ova said adi t section of frequcn above the upper limit frequencies used in the transmission of low signaling; currents.

in a signaiing system, a. plurality of transmission lines adapter; to transmit voice frequency signaling currents each transmission line comprising aplurelity oi SOCiums least one of which is adapted to transmit high frequency currents oi? the order used for carrier transmission and another section oi which is incapable of efi'cctively transmitting frequencies suhstantially higher than voice frequencies, aucl means to interconnect saioi lincs at stations intermediate the terminal stations thereof for the transmission of carrier ircqueucics from a high frequency section of one line to a high frequency section oi another line While maintaining the other sections of ihe lines electrically separate Wifih mega/(i to the transmission of voice frequency signaling currents saii'l means including an apparatus adapts-cl to sulistsntislly supPress voice frequency signaling currents while freely 

